1. Field of the Invention
The present invention relates to integrated circuits and to voltage regulators disposed on integrated circuits. More particularly, the present invention relates to negative voltage regulators for integrated circuits and negative voltage regulators having trimmable settings.
2. The Prior Art
Existing voltage regulator circuits often include a comparator having a non-inverting input coupled to a voltage reference source and an inverting input coupled to a voltage divider having one end coupled to a positive voltage potential and another end coupled to a negative voltage potential. Such a portion of a voltage regulator circuit is shown in FIG. 1, in which comparator 10 has its non-inverting input coupled to a reference voltage VREF and its inverting input coupled to a series resistor network including a first resistor 12 and a second resistor 14 connected between VCC and a negative potential VNEG. The connection to the inverting input of comparator 10 is made at the common terminals of resistors 12 and 14. The output of comparator 10 may be used in known ways to control the output voltage level of a negative-voltage charge pump.
In any given individual circuit such as the one depicted in FIG. 1, the voltage divider formed from resistors 12 and 14 may be “off” due to process variations and temperature, thus giving rise to errors in output voltage. In addition, the voltages presented to the inverting and non-inverting inputs of the amplifier in the circuit of FIG. 1 have no direct relationships to one another, thus introducing another potential source of output voltage error in a voltage regulator circuit employing such circuits.